1. Field
The present invention relates to impact protection, and more specifically, to impact protection for the head.
2. State of the Art
An impact to a moving head can cause the head to rapidly decelerate, while inertia keeps the brain travelling forward to impact the inside surface of the skull. Such impact of the brain against the skull may cause bruising (contusions) and/or bleeding (hemorrhage) to the brain. Therefore, deceleration of the head is an important factor to consider in determining the severity of brain injuries caused by impact to the head.
In all types of impacts to the head, the head is subjected to a combination of linear acceleration and rotational acceleration. Linear acceleration is considered to contribute to focal brain injuries, while rotational acceleration is considered to contribute to both focal and diffuse brain injuries.
Helmets may be used to protect the head from impacts. However, all helmets add at least some added mass to the head of its wearer. As discussed in greater detail below, adding mass to a helmet can increase the rotational acceleration and deceleration effects to the head and brain as compared to a helmet of a smaller mass.
Various impact protection technologies exist that have been proposed for use in helmets to address linear and/or rotational acceleration. Such technologies include Omni Directional Suspension™ (ODS™), Multiple Impact Protection System (MIPS®), SuperSkin®, and 360° Turbine Technology.
In a helmet with Omni Directional Suspension™ (ODS™) the outer shell and the liner are separated by ODS™ components. However, the ODS™ components add mass and bulk to the helmet. Also, the ODS™ components include hard components adhered to the inside of the outer shell. As a result, the ODS™ system requires the use of a hard and stiff liner to accommodate the hard components. Moreover, there is a possibility of individual ODS™ components detaching due to wear and tear.
In a helmet that incorporates the MIPS®, the helmet includes an outer shell, an inner liner, and a low friction layer. The low friction layer is located on the inside of the foam liner against the head, such that the shock absorbing foam liner is not in direct contact with the head. However, the use of the friction layer and its attachments reduces the ability of the helmet to effectively absorb an impact force. Moreover, MIPS® technology adds mass and bulk to the helmet.
In a helmet with SuperSkin®, a layer of a membrane and lubricant is applied to the outer shell of the helmet. The layer reduces friction between the outer shell and the impacting surface thereby reducing angular (rotational) effects on the head and brain.
In a helmet with 360° Turbine Technology multiple circular turbines are located on the inside of the foam liner against the head. While the technology adds minimal mass to the helmet, portions of the turbines may dislodge from wear and tear and, therefore, may not provide protection to the wearer of the helmet during an impact.
With the exception of SuperSkin® Technology, the above-mentioned helmet technologies do not take into account the whole thickness and mass of the helmet as a factor in limiting deceleration. Also, the above-mentioned helmet technologies encourage the incorporation of harder and stiffer liners (expanded polystyrene foam and other foams). However, harder and stiffer liners may be detrimental to a helmet's effectiveness to absorb translational and angular impact forces.